The population of patients entering the End-Stage Renal Disease (ESRD) Program in the United States (US) has grown each year since inception of Federal funding for the program. In 1990 the estimated cost to Medicare was over $5 billion and nearly 200,000 patients were receiving treatment. The major modality of therapy for this population is in-center hemodialysis (HD). Recent analysis of the HD population in the US has revealed disturbingly high mortality rates (23.4%) and marked reduction in life expectancy compared to the general population. Other countries have reported much lower mortality rates in their HD populations. Whether the US HD population can be compared to that of other countries remains a question. Reports from other countries reveal the amount or adequacy of HD received by patients tends to be greater than in the US. This fact raises the question whether adequacy of HD is a major contributor to the excess mortality of US patients. The NIH has instituted a major study to address these issues called the Mortality and Morbidity in HD (MMHD) Study. This is a five year multi-center study of patients randomly assigned to l of 4 different HD prescriptions. The different prescriptions for this study include varying adequacy of HD (KT/V of l versus KT/V of 1.4) and two different hemodialyzer membranes (a bioincompatible versus biocompatible membrane). Thus, patients will be randomized to l of 4 different protocols. Mortality will be measured as well as secondary outcomes such as hospitalizations and quality of life. This proposal is to apply to become 1 of 15 "Clinical Centers" for this study. This application demonstrates that the University of Rochester has the expertise and a sufficient HD patient population to satisfactorily recruit patients and complete this study.